1. Field
This disclosure relates to an organic solar cell and method of making the same.
2. Description of the Related Art
A solar cell is a photoelectric energy conversion device which converts solar energy into electrical energy. Solar cells have drawn attention as a pollution-free next-generation energy source.
The solar cell can be classified as an inorganic solar cell or as an organic solar cell, depending on the material of a thin film used in the cell. Because an organic solar cell uses various organic semiconductive materials in relatively small amounts, it may be manufactured with a lower cost relative to an inorganic solar cell. In addition, because the thin film of an organic solar cell is fabricated in a wet process, the organic solar cell can be more easily fabricated.
In general, an organic solar cell is classified as a bi-layer p-n junction type of organic solar cell or a bulk heterojunction (“BHJ”) type organic solar cell, depending on the structure of a photoactive layer. The bi-layer p-n junction type of organic solar cell may include a photoactive layer that includes a p-type semiconductive thin film and an n-type semiconductive thin film, while the BHJ type organic solar cell may include a photoactive layer in which an n-type semiconductor and a p-type semiconductor are blended with each other.
The bi-layer p-n junction-type organic solar cell is shown in FIG. 1. Referring to FIG. 1, an organic solar cell 100 includes a substrate 101, an indium tin oxide (“ITO”) anode 103, a photoactive layer 111, and a cathode 105. The photoactive layer 111 includes a p-type semiconductor thin film 107 and an n-type semiconductor thin film 109. The p-type semiconductor forms an exciton 117, which includes an electron 113 and a hole 115, when excited by light. The exciton is separated into an electron 113 and a hole 115 in a p-n junction region. The separated electron 113 and hole 115 respectively move toward the n-type semiconductive thin film 109 and the p-type semiconductive thin film 107 and are then collected in the cathode 105 and the anode 103, so that they can be used as electrical energy.
A solar cell desirably has high efficiency to produce as much electrical energy as possible from a given amount of solar energy. In order to increase the efficiency of a solar cell, it is important to generate numerous excitons inside a semiconductor and also to bring the produced charge to the outside without a loss.
However, while not wanting to be bound by theory, it is understood that charges may be mainly lost when the produced electrons and holes recombine. Accordingly, many methods of delivering the produced electrons and holes to an electrode without loss have been suggested. The suggested methods generally call for an additional process, and thus undesirably increase manufacturing cost. Thus, there remains a need for materials and methods that provide improved charge separation.